Shielding apparatus of metal plates strap-mounted on cathode ray tube for shielding against external magnetic fields

ABSTRACT

Apparatus for shielding cathode ray tubes, particularly color picture tubes, from the effect of the earth&#39;&#39;s and other external magnetic fields. The shielding apparatus comprises a series of overlapping steel sheets, pressed together and against the tube structure by resilient fasteners. These sheets and fasteners are secured to a strap which is tightened around the circumference of the cathode ray tube, near the front thereof, and shaped and disposed for securement to the inside of a cabinet enclosing the tube.

[56] References Cited UNITED STATES PATENTS 3,431,454 3/1969 Sanders................ 315/8 Primary Examiner-John Kominski Assistant Examiner*-V. L. Lafranchi Attorney-Carl H. Synnestvedt g cathode ray tubes, particularly color picture tubes, from the effect of the earths and other external magnetic fields. The shielding apparatus comprises a series of overlapping steel sheets, pressed together and John P. Uetz Philadelphia, Pa. [21] Appl. No. 771,214

Oct. 28, 1968 [45] Patented Feb. 16, 1971 Philco-Ford Corporation Philadelphia, Pa. a corporation of Delaware STRAP-MOUNTED 0N CATHODE RAY TUBE FOR United States Patent [72] Inventor [22 Filed [73] Assignee [54] SHIELDING APPARATUS 0F METAL PLATES ABSTRACT: Apparatus for shieldin against the tube structure by resilient fasteners. These sheets and fasteners are secured to a strap which is tightened around the circumference of the cathode ray tube, near the front thereof, and shaped and disposed for securement to the inside of a cabinet enclosing the tube.

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SHIELDING APPARATUS OF NIETAL PLATES STRAP- MOUNTED ON CATI-IODE RAY TUBE FOR SHIELDING AGAINST EXTERNAL MAGNETIC FIELDS BACKGROUND OF THE INVENTION Color picture tubes must be shielded from effects of the terrestrial field and other external magnetic fields. Heretofore this was done by a unitary, annular member of magnetic material, which generally was constructed as a welded or riveted structure in the approximate form of a truncated cone or pyramid, or sometimes use was made of a flexible ring of steel foil held to the tube by adhesive. Such a riveted or welded pyramid or conelike member proved cumbersome and expensive. If the construction was made in a more simple form, for example as a flat and rigid plate, it was very inefficient as a shield, and required a large and heavy coil for degaussing. The flexible adhesive-fastened shield was most closely joined to thetube, and therefore magnetically most efficient, but such a shield caused difficulties when the tube required servicing or repair.

It is the object of this invention to overcome the difficulties and shortcomings of prior art structures by providing shield apparatus of light weight, low cost, high efficiency, and which is easy to attach and detach.

NATURE OF THE INVENTION According to the invention, individual sheets of steel or the like are held in partly overlapping position, one in surface contact with the other where they overlap, and all in suitable contact, either direct or indirect, with the picture tube. The resulting apparatus shares characteristics of the built-up or riveted cone structure, and also shares advantages of the adhesivefastened foil ring, but avoids the shortcomings of the prior devices. The plates or sheets used according to the invention need not be permanently welded, riveted or bolted. Instead, and more economically, l use a system of simple, resilient fastening means to pressthe several steel sheets against the tube, preferably with resilient padding underlying the sheet structure, and also to press mutually overlapping parts of the sheets against one another. These sheets and fasteners are secured to a strap. The strap in turn is tightened around the periphery of the cathode ray tube, and would be secured to the inside of a cabinet (not illustrated). By means of this construction the invention provides high shielding efficiency while facilitating service work.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a perspective view of the new shield, fastened to a picture tube structure.

FIG. 2 is a fragmentary, sectional and slightly enlarged view, taken along line 2-2 in FIG. 1.

FIG. 3 is a plan view of sheet elements suitable for use in the new shield, showing them in the form that they have before they are applied to the tube structure.-

DETAILED DESCRIPTION As shown in FIG. 1, picture tube P has annular shield mounted on the rear surface of its bulb, the central configuration of the shield being of such form and size that central portions of the tube extend rearwardly through it and that the mounting of high voltage lead-in V on the bulb, and of deflector coils D on tube neck N, is not impeded by the presence of the shield elements. The new shield, as illustrated, comprises top sheet or segment ll, right and left side segments 12, 13, and bottom segment-l4, all made of magnetic material such as magnetically highly permeable but substantially nonr'etentive steel, and all held together and to corresponding parts of the tube by extension springs 15, 16, l7, 18. As shown in the drawing, the invention provides corner portions 19, of top tively. Similar relationship is provided by springs l6, 18 for corner areas 23, 24 of bottom segment 14, which overlap corresponding areas 25, 26 of the side segments. In order to make sure that the overlapping areas of the several segments are pressed against one another and against the tube, as is required for efficient magnetic shielding, the four extension springs connect the four corner areas of the shield segments to suitably chosen parts of support structure which is located at the front end of the tube and comprises a tube mounting strap 27.

This strap, as shown, has end brackets 28, 29 interconnected by bolt 30 to fasten the strap securely to the circumference of picture tube P, and the strap also holds the four shield segments, 11 to 14, against rearward displacement of these segments. For this purpose the segments have forwardly extending angle portions or tabs, which are best shown in FIG. 3 and are numbered 31, 32, 33, 34. It is preferred to make these tabs shorter than the segments, so that recesses 35, 36

are formed adjacent corner portions 19, 20, 23 and 24,

thereby facilitating the required bending of the segments when they are applied to the tube. The extension springs 15 to 18 interconnect shield apertures 37, disposed in offset parts 38 of comer portions of the top and bottom segments, with lanced hooks 39 formed on strap 27, said hooks projecting through apertures 40, 41 in side segment tabs 32, 33. Some of these hooks also serve to hold these tabs to strap 27, as is shown in FIG. 1 at 40, while fasteners 42 are provided to hold top and bottom segment tabs 31, 34 to this strap. Additional fasteners 43 can be used for holding the latter segments in position while the different springs are being applied to them. Side seg ments 12, 13, which are interchangeable have recesses 44 (FIG. 3),for brackets 28, 29 of strap 27 (FIG. I), while interchangeable top and bottom segments ll, 14 each have a recess 45 for high voltage button V.

The segments can be fabricated as generally flat sheeting with such outline at 35, 36 (FIG. 3) as to facilitate bending of the sheet structure while adapting it to the tube surface. When the retaining springs are applied, they cause such bending, for example bending of corner area- 20 onto 21, corresponding to the shape of the tube, thereby providing adequate magnetic unity of the seal ring.

As best shown in FIG. 2, a resilient cushion 45--made for example of foam rubber or of a composition of rubber and cork or the like-is provided below the sheeting, and especially below every pair of mutually overlapping corner areas, such as 20 and 22. These cushions, interposed between the sheeting and the underlying tube structure P, facilitate the mutual contacting of wide surface areas on the sheet segments, thereby enhancing the magnetic shielding effect.

A conventional degaussing coil C, with connector X, is provided. Holders, some of them shown at H, hold this coil in proper position with respect to the assembled shield and the tube. Of course the entire tube and its attachments are held by suitable mounting means, secured to strap 27 some of which are shown at M in FIG. 1. These and similar parts of the unit are not believed to require detailed description at this point.

It will be obvious from the foregoing description that the new shield segments can be formed, applied and removed, as well as reinstalled, by techniques of the utmost simplicity. When installed or reinstalled in a tube, the new shield fits the tube configuration as closely as is required for efficient shielding, while it avoids the need for heavy and cumbersome, permanently welded pyramid structures and the like and also avoiding the use of delicate and nonreplaceable shielding, formerly provided by cemented foil materials.

Iclaim:

1. Apparatus for shielding a cathode ray tube from external magnetic fields, such as that of the earth, comprising: a strap extending around the circumference of the tube near the front thereof; means to interconnect ends of the strap and thereby sheet 11, resiliently held by springs l5, 17, in overlying rela- .material, each marginally held to said strap and extending arrangement on the back of the tube, and wherein said spring means are extension springs, each extending from one of said corner structures diagonally to a portion of said strap adjacent another corner, said extension springs crossing one another on opposed sides of the back of the tube. 

1. Apparatus for shielding a cathode ray tube from external magnetic fields, such as that of the earth, comprising: a strap extending around the circumference of the tube near the front thereof; means to interconnect ends of the strap and thereby securely to fasten the strap to said tube around its circumference; a series of overlapping sheets of flexible magnetic material, each marginally held to said strap and extending therefrom to cover back portions of the tube; spring means engaging said sheets and said strap to press the sheets against one another and against the tube; and means providing for rigid securement of said strap, and thereby said tube and shield means, to a supporting structure.
 2. Apparatus as described in claim 1 wherein said overlapping sheets have corner structures disposed in quadrilateral arrangement on the back of the tube, and wherein said spring means are extension springs, each extending from one of said corner structures diagonally to a portion of said strap adjacent another corner, said extension springs crossing one another on opposed sides of the back of the tube. 